Recently, attention focuses on a so-called white-color Light Emitting Diode (LED) in which a yellow fluorescent material such as YAG:Ce is combined with a blue LED to emit white-color light by a single chip. Conventionally, the LED emits red, green, or blue light in monochromatic form, and it is necessary that plural LEDs emitting monochrome wavelengths are driven in order to emit the white-color light or intermediate-color light. However, currently, the combination of the light emitting diode and the fluorescent materials removes the trouble to obtain the white-color light with a simple structure.
An LED lamp in which the light emitting diode is used is applied to various display devices of a mobile device, a PC peripheral device, an OA device, various switches, a light source for backlight, and a display board. In the LED lamps, there is a strong demand for high efficiency. Additionally, there is a demand for high color rendering in general-purpose lighting applications, and there is a demand for high color gamut in backlight applications. High efficiency of the fluorescent materials is required for the purpose of the high efficiency of the LED lamp, and a white-color light source in which a fluorescent material emitting blue excitation light, a fluorescent material excited by blue light to emit green light, and a fluorescent material excited by blue light to emit red light are combined is preferable to the high color rendering and the high color gamut.
However, when plural fluorescent materials are used, luminous efficiency is degraded by reabsorption between the fluorescent materials. Particularly, when white-color light is obtained by a combination of the plural fluorescent materials, the problem becomes obvious by shortening a distance between the fluorescent materials.